Some, not all, motherboards use this mechanism to detect the presence of cards during POST. Down-plugging an x16 card in an x1 connector on these motherboards results in a system that does not boot or does not detect the card. The solution is to simply short pins A1 and B17 to do exactly what a real x1 card does.

Is needed when sometimes does not work the card with riser cables. In this way will work. i think that 7970 will work with pci-e extender only if it is jumpered the bitcoin mining talk about same problem with their rigs.